As is well known in the art, in a refrigeration unit utilizing the vapor compression cycle, a compressor circulates a refrigerant from an evaporator through a condenser and an expansion valve and back to the evaporator. The refrigeration unit also includes a housing defining a volume of air in which the temperature is to be controlled. For example, walk-in housings for commercial applications are well known in the art. The refrigeration unit may be a cooler or a freezer.
The evaporator typically is included in an evaporator assembly, which includes one or more fans which are rotated to circulate air in the housing, and in particular, to move air through the evaporator. Typically, the refrigeration unit includes a thermostat positioned in the housing for regulating the temperature of the air inside the housing within a desired range of temperatures. As is well known in the art, the thermostat generates signals which cause activation or de-activation of the compressor, as required to maintain the temperature of the air in the housing within the desired range. However, in the prior art, the fans typically are rotated at a substantially constant speed, regardless of whether the compressor is activated.
In the prior art, the thermostat often controls the operation of the compressor via a liquid line solenoid (i.e., a solenoid valve subassembly), which controls the flow of the refrigerant into the evaporator. A typical solenoid control circuit 44 is schematically illustrated in FIG. 1. (As will be described, the remainder of the drawings illustrate the present invention.) As shown in FIG. 1, in the prior art, a fan control circuit 52 and the solenoid control circuit 44 are not operably connected.
For example, a typical prior art solenoid control circuit 44 includes two wires (identified as L1 and L2, which may be a live and a neutral conductor), and a thermostat 30 which completes the solenoid control circuit 44 when the temperature of the air in the housing (not shown) is above a predetermined cut-in temperature, as is known. Upon its energization, the solenoid valve included in the solenoid valve subassembly opens, and while energized the valve remains open, permitting the refrigerant to circulate. As is well known in the art, after the refrigerant passes through the evaporator, the refrigerant is drawn back to the compressor.
Once a predetermined cut-out temperature is reached, the thermostat 30 opens the solenoid control circuit. Upon its de-energization, the solenoid closes, preventing circulation of the refrigerant. The refrigerant which is in the evaporator when the solenoid closes is drawn out of the evaporator by the compressor, i.e., the compressor continues to operate for a limited time. Once substantially all the refrigerant has been removed from the evaporator, a pressure switch opens an electrical circuit (not shown) to the compressor, and the compressor is de-activated, as is known. While the compressor is de-activated, the temperature of the air in the housing gradually increases, due to transfer of heat from outside the housing to its interior.
A typical evaporator assembly includes a number of fans driven by a number of electric fan motors respectively. However, it will be understood that, to simplify the description herein, reference is generally made to an evaporator assembly including a single fan motor rotating a fan.
The prior art fan control circuit 52 includes only first and second conductors L1, L2, i.e., a fan motor 21 operates when there is a sufficient predetermined voltage between the first and second conductors. While the prior art fan motor is energized, it operates at a substantially constant speed, because there is a substantially constant voltage provided between the first and second conductors while the prior art refrigeration unit operates, i.e., regardless of whether the compressor is activated. As noted above and as schematically represented in FIG. 1, the prior art fan control circuit 52 (which controls one or more fan motors 21) is independent of the prior art solenoid control circuit 44.
As is known, the electrical power supplied may be 230V or 120V. If 120V power is provided, then L1 and L2 are live and neutral conductors respectively. If 230V power is provided, then L1 and L2 are both considered live. Accordingly, for the purposes hereof, L1 and L2 are referred to generically hereinafter as a “first” and a “second” conductor respectively.
In the prior art and as described above, the fans in the evaporator assembly typically are rotated at a substantially constant speed, regardless of whether the compressor is operating or not. This is done because some air circulation in the housing while the compressor is de-activated is desirable, to maintain a substantially uniform air temperature inside the housing (i.e., while the air temperature inside the housing gradually increases over time).
Also, in a cooler, when the compressor is de-activated (i.e., the thermostat has cycled off), air circulation melts frost on the fins in the evaporator, i.e., the air circulation serves to defrost the refrigeration unit.
However, it appears that the benefits of air circulation while the compressor is de-activated would be available if the fans rotated at reduced speed(s). Accordingly, operating the fans in the evaporator assembly at a substantially constant speed is wasteful, to the extent that more energy is consumed in rotating the fans than is necessary to achieve the benefits of air circulation within the housing.